A body of airplane plywood (1.5 mm) can be made without a mold. This is a big advantage for doing it yourself but a major constraint in the design of the body shape too. A plywood sheet can not be bent into a sphere. In mathematical terms: the shape has to be developable.

The aerodynamic drag of developable shape may not be as low as that of a free formed shape. This is the compromise that I make to simplify the building and reduce the body mass.

I developed the sheets of my first velomobile with both a 1:5 and finally a 1:1 model. I simply wrapped paper sheets around curved panels. But this job can be done with a computer model too (for instance with the 3d surface modeler Rhino). I even developed a computer program in Matlab to do this. There is specialized software for hull design: Pilot3D, Delftship.

I was involved in the development of the do it yourself Alleweder velomobile at the Flevobike company in 1992. It was my job to improve and adapt the design of Bart Verhees. Bart Verhees is a very practical engineer and an experienced airplane designer. His Alleweder velomobile is build like an airplane: riveted aluminum sheet. At that time I saw the beautiful shapes that are possible using bent sheet only. And this idea never left me.

The electric machine

Together with designer Ronald Meijs we developed an electric car. It was made of an aluminum-polypropylene sandwich sheet (0.2-2-0.2 mm). This was a new material of Hoogovens named Hylite. It was aimed at the automotive industry.

Me and my first plywood car on a trip to Boulonge sur Mer

But my true love is human power and a year later I travelled to France in my first plywood velomobile. It was a 'head in' design and on that trip a learned that the fun of cycling is to feel the air flow along your head. But the concept of a velomobile of airplane plywood was proven. I made a new head out design which was build by Paddy Milford. It is has been hanging in my garage for 10 years now but recently Sjaak Bloemberg is working to get it on the road.

Wood is a very interesting material for velomobiles because of its low density. In the construction of the velomobile body the sheet stiffness is more important than its strength. The stiffness of the sheet is very much determined by its thickness. On stiffness relative to mass only sandwiches of alternative materials like carbon-aramid-epoxy with foam can compete with birch plywood. But building sandwiches is laborious and expensive and it is only recently that velomobile manufacturers offer bodies with sandwich sheet. For your information I will list some densities (kg/dm^3): birch plywood 0.7, aluminum 2.7, glass fiber 2.55, carbon fiber 1.75-1.95, polyester 1-1.45, epoxy 1.1-1.3. Look at the site of Jan Hermhart for an example of plywood in aeroplanes.

My aluminum Alleweder was over 30 kg, my first plywood velomobile 27 and the second will be around 23 kg ! As soon as the second prototype has travelled its first 100 km I will get back to you. Let me know if you would like to be involved !